Clarified docs around compute instance networking

[melinath]

Related to hashicorp/terraform-provider-google#10133. Made docs for networking more closely match each other & https://cloud.google.com/compute/docs/reference/rest/v1/instances

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 8 insertions(+), 4 deletions(-))
Terraform Beta: Diff ( 2 files changed, 9 insertions(+), 5 deletions(-))

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccDatasourceGoogleServiceNetworkingPeeredDnsDomain_basic|TestAccServiceNetworkingPeeredDNSDomain_basic You can view the result here: https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=208702